Over the years, many implantable devices have been developed to monitor medical conditions and deliver therapy to a patient. Such devices included electrical stimulation devices for stimulating body organs and tissue to evoke a response for enhancing a body function or to control pain, and drug delivery devices for releasing a drug bolus at a selected site. Other more passive implantable and wearable medical devices have been developed for monitoring a patient's condition.
Chronically implanted cardiovascular devices for monitoring cardiovascular conditions and providing therapies for treating cardiac arrhythmias have vastly improved patients quality of life as well as reduced mortality in patients susceptible to sudden death due to intractable, life threatening tachyarrhythmias. As implanted device technology has grown more sophisticated with capabilities to discover, monitor and affect more patient conditions (including otherwise life threatening conditions) patients have enjoyed freedom from hospital or home confinement or bed rest. However, the improved mobility brings with it the need to maintain communications with the patient and the implanted device.
Early in the development of cardiac pacemakers, patient follow-up to monitor pacemaker operation was facilitated by telephonic transmissions of skin surface ECGs in real time to a physician's office employing such systems as the MEDTRONIC.RTM. TeleTrace.RTM. ECG transmitter. Over time, various patient worn, ambulatory ECG and device monitors have been developed for providing ECG data for remote analysis of cardiac arrhythmias. Also, the remotely programmable modes of operation of implantable medical devices increased, and programming methods improved.
In current arrhythmia control devices, (e.g. cardiac pacemakers, and pacemaker-cardioverter-defibrillators) a relatively wide range of device operating modes and parameters are remotely programmable to condition the device to diagnose one or more cardiac arrhythmia and deliver an appropriate therapy. In cardiac pacemakers, the pacing rate in one or both heart chambers is governed by algorithms that process the underlying cardiac rhythm as well as physiologic conditions, e.g. patient activity level and other measured variables, to arrive at a suitable pacing rate. The pacemaker operating modes and the algorithm for calculation of the appropriate pacing rate are programmed or reprogrammed into internal memory by accessing the implanted pacemaker's telemetry transceiver with an external programmer. Even the diagnosis of a tachyrhythmia requiring delivery of a treatment therapy and the therapies to be delivered may now be governed by operating modes and algorithm parameters that can be programmed into and changed using such a programmer.
Such implanted devices can also process the patient's electrogram and any measured physiological conditions employed in the diagnosis and store the data, for subsequent telemetry out on interrogation by the external programmer. The telemetered out data is analyzed and may be employed to establish or refine the operating modes and parameters by a doctor to adjust the therapies the device can deliver. In general, the manner of communicating between the transceivers of the external programmer and the implanted device during programming and interrogating is referred to as telemetry.
Initially, when programming techniques were first devised, the paramount concern addressed related to patient safety. Safeguards addressed the concern that the patient could be put at risk of inadvertent mis-programming of the implanted device, e.g. by stray electromagnetic fields. For this reason, and in order to avoid high current consumption that would shorten the implanted device battery life, telemetry operating range was extremely limited. In systems continuing to the present time, telemetry has required application of a magnetic field at the patient's skin over the implanted device to close a reed switch while RF programming or interrogating commands are generated to be received by the implanted device transceiver. The programming or interrogating commands are decoded and stored in memory or used to trigger telemetry out of stored data and operating modes and parameters by the implanted device transceiver.
As stated at the outset, one of the rationales and attributes of implanted medical devices of the type described, is that the patient is allowed to be ambulatory while his medical condition is monitored and/or treated by the implanted medical device. As a further safety precaution, "programmers" (devices capable of programming all the operating modes or functions of the implanted device and for initiating interrogation through the telemetry system) are generally not provided to the patients. Patients are periodically examined and device interrogation is conducted by the physician using the external "programmer" during follow-up visits to the physicians office or clinic. This limits the frequency of monitoring and may require certain patients to remain close to the physician's office.
Emergency conditions (device failure, physiologic variable changes resulting in inappropriate therapy, transient conditions/problems) may require additional monitoring or follow-up.
The short range of conventional device telemetry is itself viewed as unduly limiting of a patient's mobility. In the medical monitoring field, longer range, continuously accessible telemetry has been sought and systems for doing so have been proposed. In U.S. Pat. No. 5,113,869 for example, an implanted ambulatory ECG patient monitor is described that is provided with longer range telemetry communication with a variety of external accessory devices to telemeter out alarm signals and ECG data and to receive programming signals. The high frequency RF signals are encoded, including the implanted device serial number, to ensure that the communication is realized only with the proper implanted device and that it is not misprogrammed.
Telemetry communication with other implanted devices, particularly drug infusion pumps or pacemaker-cardioverter-defibrillator devices, to initiate or control their operation is also disclosed. Communication between the implanted AECG monitor and an external defibrillator is also suggested through low current pulses transmitted from the defibrillator paddles through the body link in order to condition the implanted AECG monitor to provide telemetry signals to the external defibrillator.
One of the external devices disclosed in the '869 patent is a wrist worn, personal communicator alarm for responding to a telemetered out signal and emitting a warning to the patient when the implanted AECG monitor has detected an arrhythmia. The patient is thereby advised to take medications or contact the physician or to initiate external cardioversion. The personal communicator alarm also includes a transceiver and may also be used to control certain functions of the implanted AECG monitor. A further, belt worn "full disclosure recorder" is disclosed with high capacity memory for receiving and storing data telemetered out of the implanted AECG monitor when its memory capacity is exhausted.
A remote, external programmer and analyzer as well as a remote telephonic communicator are also described that may be used in addition to or alternately to the personal communicator alarm and/or the full disclosure recorder. The programmer and analyzer may operate at a distance to the implanted AECG monitor to perform programming and interrogation functions. Apparently, the implanted AECG may automatically transmit a beacon signal to the programmer and analyzer to initiate an interrogation function to transmit data to the programmer and analyzer on detection of an arrhythmia or a malfunction of the implanted AECG monitor detected in a self-diagnostic test. Or by setting a timer in the personal communicator alarm, the implanted AECG monitor may be automatically interrogated at preset times of day to telemeter out accumulated data to the telephonic communicator or the full disclosure recorder. The remote telephonic communicator may be part of the external programmer and analyzer and is automatically triggered by the alarm or data transmission from the implanted AECG monitor to establish a telephonic communication link and transmit the accumulated data or alarm and associated data to a previously designated clinic or physician's office through a modem.
The combination of external devices provided to a given patient is at the discretion of the physician. It is preferred that at least the patient be provided with the external programmer and analyzer including a communications link.
A similar programmer/interrogator for an implanted pacemaker-cardioverter-defibrillator device is disclosed in U.S. Pat. No. 5,336,245, wherein the data accumulated in the limited capacity memory implanted device is telemetered out to a larger capacity, external data recorder. The accumulated data is also forwarded to a clinic employing an auto-dialer and FAX modem resident in a personal computer-based, programmer/interrogator.
In each of these disclosed systems, presumably, the patient is able to communicate with the physician's office or clinic contemporaneously with the transmission of data by modem. In all such telemetry systems for programming an operating mode or parameter or interrogating accumulated patient data or device operating modes and parameters, the patient is located within a short range, typically within sight, of the remote devices, particularly the remote programmer. If the patient is out of range of the programmer and an attached telephone system, the security of the patient is diminished. Consequently, at risk patients are advised to remain close by to the programmer and telephone for their safety.
The performance over time of implanted medical devices in the implant population is informally monitored by the periodic patient follow-ups employing the telemetry system conducted by the physician and the reporting of device malfunctions from the physician to the device manufacturer. Moreover, operating algorithm improvements developed over time to counter adverse device performance reports or to simply improve device function are provided to physicians to employ in re-programming the implanted devices at the next patient follow-up.
Although significant advances have been made in allowing patient's who are dependent on implanted medical devices to be ambulatory and still allow for monitoring of the device operation or the patient's underlying condition, a need remains to expand patient security while allowing the ambulatory patient to range widely. Telemetry systems in current use require prepositioning of the telemetry head over the implanted medical device, although the telemetry systems described above may offer the possibility of telemetry at a distance of several meters. In any case, such telemetry systems cannot communicate patient device information (uplink telemetry) or accept re-programming (downlink telemetry) when the patient is in remote or unknown locations vis-a-vis the physician of medical support network. In certain patient conditions, the inability to communicate with the medical implant can significantly increase patient mortality or cause serious irreversible physical damage.